1. Field of the Invention
The present invention relates to a solid state image sensor, and more particularly, to a solid state image sensor and a method for fabricating the same having a wide light reception area.
2. Discussion of the Related Art
A conventional solid state image sensor will be explained with reference to FIGS. 1 and 2A-2E. FIG. 1 illustrates a layout of the conventional solid state image sensor, and FIGS. 2A-2E illustrate relevant sections of the conventional solid state image sensor shown in FIG. 1.
The conventional solid state image sensor has a 4-phase clock applied thereto for transfer of image charges generated in a photoelectric conversion region 1. As means for applying a clock signal, two layers including first and second transfer lines 2 and 3, respectively, are insulated from each other by an insulating film 4, between a plurality of the photoelectric conversion regions 1. The underlying first transfer line 2 is insulated from a semiconductor substrates by another insulating film 6.
Of the 4-phase clock signals applied to the transfer lines 2 and 3, clock signals .phi.1 and .phi.3 are applied to the first transfer line 2, and clock signals .phi.2 and .phi.4 are applied to the second transfer line 3.
Each of the first and second transfer lines 2 and 3 includes transfer electrodes formed repeatedly in transfer line regions to correspond to the photoelectric conversion regions 1. Upon repeated application of the .phi.1, .phi.2, .phi.3 and .phi.4 clock signals to the first and second transfer lines 2 and 3 having the aforementioned system, respectively, a potential in the underlying transfer line region is changed to transfer the image charges therein toward one direction.
However, in the formation of the first and second transfer lines for applying the 4-phase clock signals in the conventional solid state image sensor, and in view of its process, since the first transfer line should be formed wider than the second transfer line for forming the second transfer line on the previously formed first transfer line, a fill factor (or aperture ratio) is reduced and, consequently, a light sensitivity is decreased. The more the pixel is packed, the more the fill factor is reduced because the number of transfer lines increases as the number of pixels increases.
Therefore, the aforementioned conventional device structure does not allow a highly packed solid state image sensor.